Jan. 18, 2012 -- Women with normal or nearly normal bone density at age 67 may not need repeat testing for about 15 years, according to a new study of nearly 5,000 women.

If bone density was normal or nearly so at the study start, "only 10% developed osteoporosis over 15 years,'' says study researcher Margaret Gourlay, MD, MPH, assistant professor of family medicine at the University of North Carolina, Chapel Hill. "Their bone density was very stable."

Osteoporosis is a leading cause of dangerous and painful fractures. A routine bone density test is recommended for women at age 65. However, guidelines are vague about how often to repeat the test, Gourlay tells WebMD. She says the new research will provide guidance for organizations that make such recommendations.

Not everyone agrees. An interval of 15 years is too long, says Felicia Cosman, MD, senior clinical director for the National Osteoporosis Foundation, who reviewed the study for WebMD. She cites flaws in the study design.

The study is published in The New England Journal of Medicine.

Bone Density Testing: Study Details

''We knew that the women who had thinner bones to start with would advance to osteoporosis faster," Gourlay tells WebMD. "The new thing we showed was a clear difference between low-risk and high-risk groups and how rapidly they developed osteoporosis."

The women were enrolled in the Study of Osteoporotic Fractures in 1986-1988, when they were aged 65 or older. They had bone density testing about two years later.

After excluding some women for various reasons -- such as having osteoporosis already or a history of fractures -- almost 5,000 women were placed into one of four groups depending on their bone density. The four groups included:

The women were followed for up to 15 years. They had two to five repeat tests.

The researchers took into account major risk factors, such as age, weight, and smoking.

The researchers estimated the time it would take for 10% of the women in each group to progress to osteoporosis. They concluded that osteoporosis would develop in:

About 15 years for those with either normal bone density or mild osteopenia

About five years for those with moderate osteopenia

About one year for those with severe osteopenia.

The study was funded by the National Institutes of Health.

The results may help women and their doctors decide how often to re-test, Gourlay says, and the findings only apply to postmenopausal women age 67 and over.

Bone Density Testing: Perspectives

The study provides valuable information to doctors and patients, says Robert A. Adler, MD, chief of endocrinology at the McGuire Veterans Administration Medical Center. He is also professor of internal medicine and epidemiology and community health at the Virginia Commonwealth University School of Medicine, Richmond. "Doctors haven't really known how soon to re-measure bone density."

He reviewed the study results for WebMD.

The findings suggest that ''those women who have this very mild version [of osteopenia], just under normal bone, probably don't need another bone density test for 15 years," says Adler, not speaking on behalf of the Veterans Administration.

The study findings may help women with normal or near-normal bone density stress less. "It will keep some people from obsessing over their bones if they have just mild osteopenia," he says.

The findings suggest doctors should focus on patients with severe osteopenia, he says. The study only included women, Adler points out. The condition is more common in women, but can also affect men. Adler reports receiving research funds to his institution from Novartis, Merck, Genentech, Amgen, and Eli Lilly, all makers of osteoporosis drugs.

Cosman has misgivings about the new research. ''This study is only a few thousand, and there are some inherent biases in the way the study was done," says Cosman, a professor of clinical medicine at Columbia University College of Physicians and Surgeons in New York, and an osteoporosis specialist at Helen Hayes Hospital, West Haverstraw, N.Y. One example, she says, is excluding those with a history of fractures.

She does agree that women with severe osteopenia should get re-tested in a year, as Gourlay suggests. However, Cosman says the other intervals are too long. Women with moderate osteopenia, she says, should be re-tested in two years, not five.

Those with normal or nearly normal density should consider another test in five years, she says, not 15.

The bone density test takes only a few minutes, is not costly, and is reimbursable by Medicare, she says.

SOURCES: Margaret Gourlay, MD, assistant professor of family medicine, University of North Carolina, Chapel Hill.Robert A. Adler, MD, chief of endocrinology at the McGuire Veterans Administration Medical Center; professor of internal medicine and of epidemiology and community health, Virginia Commonwealth University School of Medicine, Richmond.Gourlay, M. The New England Journal of Medicine, Jan. 19, 2012.Felicia Cosman, MD, senior clinical director, National Osteoporosis Foundation; professor of clinical medicine, Columbia University College of Physicians and Surgeons, New York; osteoporosis specialist, Helen Hayes Hospital, West Haverstraw, N.Y.